Data can be transmitted electromagnetically between a transmitting and a receiving antenna. The transmitter encodes the data into a sequence of symbols selected from a signal constellation. The transmitting antenna transmits the symbols and the receiving antenna detects the symbols.
Interference from noise and reflections corrupts the symbols received by the receiving antenna. For a maximum-likelihood detector, the receiver can compare the received signal with the expected received signal for all of the symbols in the constellation. The expected received signal that most closely matches the actually received signal provides the detected symbol.
A measurement of the characteristics of the communication medium helps proper symbol detection. In one example, the transmitter periodically transmits a known pattern of symbols to the receiver and the receiver uses the known pattern to determine the characteristics, such as multiple signal propagation paths, of the communication medium.
The data transfer rate of electromagnetic communication increases by transmitting multiple symbols in parallel from multiple transmitting antennas. The detection of the multiple transmitted symbols improves by receiving the symbols with multiple receiving antennas.
For maximum-likelihood detection with multiple transmitting antennas, the number of possible combinations of symbols transmitted in parallel is the degree of the constellation raised to the power of the number of transmitting antennas. Evaluation of all possible combinations is infeasible for higher order modulations and a large number of antennas.
The present invention may address one or more of the above issues.